Field of Application
The present invention relates to integrated electronic devices for detecting one or more parameters relating to the presence of water, humidity, acidity/basicity of an environment surrounding the device. A monitoring system, and a method for detecting such parameters are also comprised in the invention, such system and method using the above-mentioned device.
Description of the Prior Art
In the field of monitoring an environment around a given monitoring point, it is very important to take into account parameters such as humidity and acidity/basicity.
If there are structures or parts of structure made of metal, in the environment to be monitored, it is also important to carry out an assessment of the state of corrosion of such metal parts.
Monitoring of solid structures, such as load-bearing structures of bridges, or also of buildings, tunnels, railways, dams, embankments, underground structures of city underground railways, etc., can be considered as an application example significant for illustrative purposes, however not being limiting. In particular, structures in building material, for example reinforced concrete, composed of concrete reinforced with metal rods can be considered.
In this context, devices and systems for monitoring different parameters, relating to forces or temperature, are known. For example, the international patent application WO 2012/084295, by the Applicant, discloses a device for monitoring, inside a solid structure, a mechanical stress and/or pressure and/or temperature, comprising an integrated detection module, in which at least one integrated sensor and the relative circuitry are included, as well as electromagnetic means for the communication to and from the outside. In WO 2012/084295, the integrated detection module comprises a passivating layer that completely coats the integrated sensor and the relative circuitry, to ensure robustness and a long operative lifetime; however, this feature prevents such devices from detecting humidity and/or acidity/basicity. The importance to detect parameters such as humidity and/or acidity/basicity is crucial, in view of a meaningful and reliable monitoring.
Designers and maintenance technicians of structures to be monitored need to assess the evolution of the degradation due to the presence of water and/or humidity. In fact, the phenomena that may cause such degradation are numerous.
As regards concrete, this is an artificial stone material composed of stone aggregates with different dimensions, referred to as inerts, joined by cement, which is an hydraulic binder, the activation of which occurs due to chemical reactions with water. Inerts have dimensions ranging from a few tenths of a millimeter to some tens of millimeters. The cement granules have a size ranging from 1 to 50 μm, and they fill the spaces that are present between the inerts, determining a solidified slurry, on the whole porous and permeable. The concrete can have different degrees of porosity and permeability, depending on its composition and the size of inerts and cement granules; however, a certain degree of porosity and permeability can be anyhow found.
Because of this fact, humidity and/or other atmospherical agents and/or water (which may in turn contain different chemical compounds in solution) penetrate into the concrete and may cause several chemical/physical phenomena, such as to degrade both the concrete, and the metal of the rods (i.e., the reinforcing steel or iron bars) present in the reinforced concrete. Among the main causes of degradation, the following ones can be mentioned.
Carbonation is due to the penetration of humidity, oxygen O2 and carbon dioxide CO2 into the cement. Such phenomenon does not involve a reduction of the robustness of the concrete, but it is very dangerous for the reinforcing iron bars. Usually, in the concrete, by virtue of the lime that is formed by hydration of the cement, the pH is strongly basic (12-14) and the iron bars are thus passivated and protected by such alkaline environment through the formation of a passivating film of iron oxide, adherent to the iron bars and not permeable, which prevents a further oxidation. However, when the outermost layer of the concrete structure, also referred to as “concrete cover”, is penetrated by CO2, lime is neutralized and calcium carbonate is formed, which decreases the pH, determining a more and more acid environment, and starting the corrosion of the iron when the pH has a value of about 8 or 7. Furthermore, the rust that is formed by the oxidation of the iron bars, causes a volume increase, determining a traction on the concrete, which may crack and even cause the release of the concrete cover layer due to the tensional load; the surfacing iron bars are thus exposed to a rapid corrosion that may cause the rapid degradation of the structure and compromise the stability thereof.
A sulphate etch occurs when the infiltrated water comprises sulphates, reacting with calcium hydrates, aluminates and silicates of the cement, thus forming gypsum, ettringite and thaumasite, thus causing bulging, cracks and releases in the concrete, or a breakage of the conglomerate.
Chloride etching is due to the ion chlorine, that is found, for example, in sea water. Chlorides cause a corrosive action on the reinforcing iron bars, which action removes the above-mentioned iron oxide passivating film and triggers a further rapid oxidation. Furthermore, sodium chloride may cause an alkali-aggregate reaction in the presence of amorphous silica, reaction which forms an alkaline silicate swelling in wet environments, and giving rise to devastating cracks. The salt, i.e., sodium chloride, is thus capable of damaging both the reinforcing iron bars, and the concrete containing reactive aggregates such as amorphous silicas. A similar degradation is caused by calcium chloride, which causes the corrosion of the reinforcing iron bars and which may further react with the calcium hydrate of the concrete, producing the calcium oxychloride hydrated, with a consequent devastating effect due to a volume increase.
The freeze-thaw cycles, due to the infiltration of water only, are a physical cause for degradation, due to the formation of ice, with a consequent volume increase (about 9%), which causes repeated pressures, that may cause cracks and crumblings in the concrete.
From what has been illustrated above, an urgent need is apparent, i.e., the need to accurately monitor both the presence of water, and humidity, and pH, and the state of corrosion of the reinforcing iron bars, by means of devices that, in turn, should be as much as possible not affected by the wear causes that are found inside the solid structure to be monitored.
In view of this, humidity sensors comprising an integrated circuit are known, based on the principle of the variation of a capacitance in a capacitor that is located outside of a passivating layer covering the integrated circuit.
However, if such known sensors were used to monitor building structures, the severe drawback of a considerable and rapid degradation of the sensor performance would occur, up to the complete unserviceability thereof, due to the corrosion of the metal electrodes of the capacitor, arranged outside of the passivating layer.
In addition, the above-mentioned known humidity sensors are not capable of detecting the parameter acidity/basicity, for example, in terms of pH, and they are not able to carry out direct and reliable assessments about the corrosion stage reached by the metal parts comprised in the structure to be monitored.
As regards the parameter acidity/basicity, pH sensors are known, i.e., detecting the concentration level of H+ ions in water, based for example on metal oxide electrodes, in which the potential difference created at such electrodes is measured, through different known possible methods: for example, in the case of the ISFET (Ion Sensitive Field Effect Transistor) there is a variation of the threshold voltage. Sensors of pH are also know, that are based on structures having an electrode that is inert with respect to the pH and an electrode that is made sensitive to the pH, by a pH sensitive layer (actually, these structures are capacitors having the pH sensitive layer as a dielectric, wherein the capacitance variations of such capacitors are measured as a function of pH).
Both types of known sensors are affected by the already mentioned drawback related to the rapid performance degradation due to the corrosion of the metal part of the sensor, when it is used inside a structure to be monitored.
Furthermore, even in this case, the known sensors to measure the pH are not capable of measuring humidity, nor of providing reliable information about the corrosion stage reached by metal parts comprised in the structure to be monitored.
Therefore, the above-mentioned prior art solutions leave unmet the need to provide sensors capable of detecting parameters of utmost importance, such as humidity and/or acidity and/or corrosion degree, preferably more than one, and which at the same time are sufficiently free from the mentioned degradation causes, so as to be suitable to be used in the widest operative conditions, for example, while being buried in building structures to be monitored.